This invention relates in general to radar weapon systems and pertains particularly to a method for firing a computerized radar weapon system upon a fast target.
Existing radar weapon systems, such as those commonly employed aboard ship, often include a computer system in combination with a gun system and a radar system for target tracking and closed-loop bullet (or other projectile) spotting. A target is fired upon by leading the target in the usual manner of firing at an intercept point ahead of the target according to target velocity and projectile flight time in an attempt to score a hit at the intercept point. The gun is aimed at the intercept point on the basis of predetermined corrections for various aim-biasing factors, such as wind and refraction, and if the target is missed the amount of the miss is measured and used to correct the aim for another attempt at another intercept point.
By this method, corrections to aim are made according to the estimated projectile trajectory.
Although effective in many respects, the foregoing method has certain limitations. For example, some fast targets, such as anti-ship missiles, have speeds of the same order of magnitude as the projectiles fired against them. When firing upon such fast targets, the target travels a considerable distance between its position when the projectile is fired and the intercept point, as well as traveling a considerable distance between two successive intercept points. Since variations often occur in aim-biasing factors from one point to another, corrections made for a miss at one of the intercept points are often in error for the other intercept point, and the target is missed again.
Furthermore, since some aim-biasing factors such as wind vary with time, predetermined corrections may be in error by the time the target is fired upon.
Thus, when engaging a fast-approaching threat, the net result of existing closed-loop aim bias correction methods is to transfer to closer range, the errors unavoidably encountered in target-tracking and projectile-spotting at long range.
One such long-range error is caused by multipath reflections of the radar signal from the underlying surface, Barton, D. K., "Low Angle Radar Tracking", Proc. IEEE, June 1974, v. 62 No. 6, pp 687-704. Another is the effect of clutter and jamming. It can be taken as a general rule that tracking errors are greater at longer ranges.
Consequently, it is desirable to have a new method for firing a radar weapon system upon a fast target.
It is desirable to have a method that compensates for or reduces susceptibility to time-dependent variations in aim-biasing factors.
It is desirable to have a method that compensates for or reduces susceptibility to space-dependent variations in aim-biasing factors.
It is desirable to have a method that does not transfer long-range tracking errors to closer-range firing.
And, it is desirable to have a method readily adaptable to existing radar weapon systems.